1. Field of the Invention
The present invention relates to a dielectric resonator device, a high frequency filter, and a high frequency oscillator which are suitable for use in high frequency electromagnetic waves (high frequency signals) such as microwaves and millimetriwaves.
2. Description of the Related Art
In general, a dielectric resonator device is known (e.g., Japanese Unexamined Patent Application Publication No. 11-239021, etc.) in which electrode films are provided on the front and back surfaces of a dielectric substrate, and a TE010-mode resonator is constituted by circular openings formed on the front and back surfaces of the dielectric substrate so as to oppose each other, with the dielectric substrate provided therebetween, and in which the front surface of the dielectric substrate is provided with a coplanar line connected to the TE010-mode resonator.
In this example of the related art, a strip central conductor of the coplanar line which is provided between grounded conductors (the electrode films) is extended into the circular openings of the TE010-mode resonator. This uses the extended central conductor as a coupling line, thus strongly coupling the coplanar line and the TE010-mode resonator.
In addition, another dielectric resonator device of the related art is also known in which a slot resonator with a grounded conductor is formed by a rectangular opening formed in an electrode film on the front surface of a dielectric substrate and a back surface's electrode film used as a grounded conductor, and in which a slot line composed of a groove is formed in the electrode film on the front surface and the slot line is connected to a rectangular slot resonator.
In the above dielectric resonator device of the related art, the mode of exciting and transmitting a high frequency signal differs among the TE010-mode resonator, the slot resonator, and the coplanar line. Accordingly, when strong coupling is established between the TE010-mode resonator or the like and the coplanar line, a problem occurs in that no load Q (Q0) of the resonator deteriorates, thus increasing the loss.
In the other dielectric resonator device of the related art, in both the slot resonator and the slot line, a high frequency signal is excited and transmitted in the TE mode. Thus, deterioration in Q0 caused by mode difference can be prevented. Although the electrode film in the contour portion (the periphery of the rectangular opening) of the slot resonator forms a short-circuited face, a leading end of the slot line is directly connected to the short-circuited face. Thus, electric field intensity at the leading end of the slot line cannot be increased, so that strong coupling between the slot resonator and the slot line cannot be obtained.